Urea is a common test used to check whether the kidney is functioning properly. It is usually done on an empty stomach in the morning because the production of urea in blood is affected by many factors, such as high protein diet, infection, fever, etc. If you eat in the morning, the urea test value may be high. If there is an abnormal result of urea value, such as an increase, it is mostly seen in renal dysfunction, and if it increases several times, it will be renal insufficiency and renal failure, which needs to be further examined in a specialized department, such as nephrology.